feat(algs): add graph class

Author: jessicayung

algorithms/graph.py

@@ -0,0 +1,40 @@
+"""
+Graph class
+
+Jessica Yung
+Jan 2018
+"""
+import numpy as np
+
+class Graph:
+    def __init__(self, adjacency_matrix, num_vertices):
+        self.adj_mat = adjacency_matrix
+        self.v = num_vertices
+
+    def is_adjacent(v1, v2):
+        return self.adj_mat[v1, v2]
+
+    def remove_vertex(v):
+        self.adj_mat[v,:] = 0
+        self.adj_mat[:,v] = 0
+
+    def find_num_islands(self):
+        num_islands = 0
+        accounted_for = np.zeros(self.v)
+        for v in range(self.v):
+            if accounted_for[v]:
+                continue
+            if not sum(self.adj_mat[v] * accounted_for):
+                num_islands += 1
+            # accounted_for[v] = True
+            indices = np.nonzero(self.adj_mat[v][v:])[0] # need [0] bc else returns a tuple
+            indices += v
+            for index in indices:
+                accounted_for[index] = True
+        self.num_islands = num_islands
+        return num_islands
+
+# Test Graph class
+# t1 = Graph([[1,1,1,0],[1,1,0,0],[1,0,1,0],[0,0,0,1]], 4)
+# print(t1.find_num_islands())
+